Oil Pressure Fuel Shut Off

[ranko_87]

Hey everyone, I've fitted semi slicks to my 20 now... and I've been told to be careful of 2 things:

 

1. Over working the brakes with increased speeds (already ordered front pads in the QFM A1RM, double the working temp of my current pads)

and

2. Oil surge as a result of increased corner speed and non baffled sump.

 

While not a solution, I am in the process of fitting an oil pressure gauge and an autometer pro warning light (idiot light)

 

I'm just concerned about the number of senders being tee'd off the oil pressure switch. There is the gauge, a idiot light sender and in the future, a 5psi electric fuel pump safety shut off switch.

 

I have a few questions,

 

1. Autometer do a 15, 30 and 50 psi idiot light sender, from my corolla manual the specs say 42psi oil pressure at 3000rpm @ 100 deg. C or 28psi at 300rpm @ 100 deg. C

so do I use a 30psi sender, which will most likey flash on at low rpm or use a 15psi sender which will most likey not come on as early, but is 15psi pressure enough at high rpm.

 

2. If I use the 15psi light sender, could i use a relay with a switching earth to cut the fuel pump? would 15 psi be low enough that the fuel pump would run as soon as the motor has kicked? If i wire the relay to swich when ground is opened, then how can i wire in bypass for when the engine cranks?

 

Cheers

 

Andrew

Edited April 27, 2010 by ranko_87

[ranko_87]

Here is what i am thinking? Will this work, I'm not auto electrician.

 

[Trev]

I was just replying to say this and had 2 windows opened and seen you had posted, Basically you need to do a voltage check from + battery to the oil pressure sender connection while the car is idling to see if it will provide enough voltage to open a relay, 15psi should be adequate, Some of the cars in the TA series run alarms at 20-25psi, Just hook it up how you have it and see how it goes.

[philbey]

You running carbs? Because a fuel pump cut off triggered by an oil pressure issue is going to have a bit of lag as you'll have a load of fuel in the fuel bowls so it wouldn't be overly useful.

 

If you install a crane/msd ignition (6AL) you could use a second stage rev limiter triggered by your oil pressure sender.

[ranko_87]

You running carbs? Because a fuel pump cut off triggered by an oil pressure issue is going to have a bit of lag as you'll have a load of fuel in the fuel bowls so it wouldn't be overly useful.

 

If you install a crane/msd ignition (6AL) you could use a second stage rev limiter triggered by your oil pressure sender.

 

The fuel pump shut off isn't really to kill the motor, just to stop the pump emptying the fuel all over the track. It is a CAMs requirment if you run an electric pump to have a shut off if the engine stalls.

 

Obviously the + battery in my diagram would actually be ignition on.

 

So you think that the resistance through the sender may be too high to ground the relay?

 

I think 20-25 PSI would be perfect but autometer only does a 15, 30 and 50. and i don't know who else might make one. Holley do a 5psi saftey shut off switch, which is all in 1. Power in, to fuel pump, and crank wire. But 5psi is a bit low for my idiot light, and i don't want to have to run 3 senders.

[philbey]

Ah okay sorry, didn't quite get what you were doing.

 

Best way to kill fuel pump is get one of the little black boxes they use for LPG cars; they have a signal from your ignition coil and when the signal stops they kill the pump after 5 seconds.

 

I think the brand I used is Peak, any auto electrician should be able to hook you up.

[Taz_Rx]

I going to agree with Philbey here and suggest some sort of ignition cut instead of a fuel cut, for several reasons:

1, It won't be instantanious as philbey mentioned. You're going to need to drian the float bowl before anything happens. Ignition cut will be instantanious.

2, For aguments sake lets say your flat to the boards around a corner so oil pressure drops a bit and triggers the fuel cut. Lets also forget about the float bowl for a second.... what effectively happen to your motor..... its leant out substantially.... at the same time its being starved of oil as well! Again, cutting the ignition won't have the same detramental effect on the motor.

3, As you've already worked out youself you're going to have a chain reaction of failure while trying to start the car and would need a bypass of the fuel cut to get it started, mind you this would be the same case if you did go for an ignition cut. Maybe an idea for the compulsary for cut you need would be to see if you can get some sort of trigger off the alternator so the fuel pump does switch on until it see 13+V!? That way when you try and start it the alternator will make some charge, switch on the fuel pump and away you.... in theory.

 

At the end of the day this whole thing is just a band aid solution for the real problem..... the lack of baffeling and/or capacity in your sump.

[ranko_87]

I going to agree with Philbey here and suggest some sort of ignition cut instead of a fuel cut, for several reasons:

1, It won't be instantanious as philbey mentioned. You're going to need to drian the float bowl before anything happens. Ignition cut will be instantanious.

2, For aguments sake lets say your flat to the boards around a corner so oil pressure drops a bit and triggers the fuel cut. Lets also forget about the float bowl for a second.... what effectively happen to your motor..... its leant out substantially.... at the same time its being starved of oil as well! Again, cutting the ignition won't have the same detramental effect on the motor.

3, As you've already worked out youself you're going to have a chain reaction of failure while trying to start the car and would need a bypass of the fuel cut to get it started, mind you this would be the same case if you did go for an ignition cut. Maybe an idea for the compulsary for cut you need would be to see if you can get some sort of trigger off the alternator so the fuel pump does switch on until it see 13+V!? That way when you try and start it the alternator will make some charge, switch on the fuel pump and away you.... in theory.

 

At the end of the day this whole thing is just a band aid solution for the real problem..... the lack of baffeling and/or capacity in your sump.

 

 

Thanks for your replies, you have made valid points.

 

I'm sort of trying to kill 2 birds with one stone and may have mislead you as to what i'm trying to do. I am only trying to get a warning light illuminate at low oil pressure (PSI yet to be determind) and have the fuel pump cut if the engine stalls but ignition is left on. (roll over or any crash really)

 

I figure if oil pressure drops below lets say 15PSI when I am at full RPM (atm only 6500) killing the engine instantly, or seeing the idiot light flash on, backing off and killing the engine isn't going to make a whole lot of difference. The damage would already be done expecially if it was due to a leak or something like that. So for the moment, i am just going to install my idiot light.

 

http://www.autometer.com/cat_accessoriesdetail.aspx?vid=158

 

Which is like having a red torch shining in your face and if it flashes up momentarily mid corner in my first race i know i have to pull the sump off and baffle it. with the added bonus of having it there to minimise damage incase of failure.

 

The fuel cut is a CAMS requirement if running an electric pump. At the moment i am running a mechanical pump so i don't have to worry about it, but if i put the wiring in place, running off the same switch the job is done for when i change to electric facet pump and side draft webers.

 

With the wiring diagram above, i would just have to link the crank wire into the 87a terminal of the fuel pump relay? Do you think the engine would get above 30psi oil pressure quick enough between releasing the key and having 30psi as to not turn off the pump?

 

Unfortuantly i have to avoid black boxes coming of the distributer as can only run electric ignition if it is concealed in the dizzy and can't run MSD etc. so even though the fuel cut has no mechanical advantage, it could cause hassles always having to explain it to scuiteneers.

 

I also wouldn't mind having a fuel pump light, given all the switches in place to have it disconnect.

[Taz_Rx]

Actually forget my alternator trigger idea, cause the load of the starter motor will drop the volts down to like 8-10 while cranking so you won't get the 13+v to trigger the pump. :)

[philbey]

Don't bother with 2 birds 1 stone, save yourself a lot of rooting around and buy a proper ignition cutoff.

 

All you need for this is a wire from your coil low voltage +ve signal to the little box mounted next to it. Depending on what sort of fuel pump you use, the relay should handle the amperage you need to run it.

 

this is the exact unit I'm talking about, basically just a purpose built relay. Brand is Peel, not Peak, any automotive store should sell them for ~50 bucks.

 

Safety Switch

CP30 Safety Switch

The safety switch incorporates relay specifically suited to high current loads eg. multiple lock offs. Able to detect light engine pulses. Moulded box designed for ease of mounting, neater appearance, terminals and circuitry is water resistant.

 

from this website:

 

http://www.peelinstruments.com.au/products.html#top

[ranko_87]

I want an oil pressure warning light which comes on earlier then the standard one so i will have the relay in place anyway. I have VDO Adjustable oil pressure sender unit ordered. It is adjustable from 20 to 60 psi. I will look through that site as it would be nice to get a shut off with a 3 second delay, and that would work for 3 second from intial ignition on.

 

This is stright from the CAMS Manual

 

"Ignition: May be of the same type, but not necessarily brand as supplied by the manufacturer for the make

and model concerned. Contact breaker points and condenser may be removed and their standard operations

performed by electronic components providing the following conditions are adhered to:

(i) All components, save for the coil, shall be an integral part of the distributor.

(ii) A maximum of two wires shall connect the low tension side of the distributor to the coil. These wires shall

be visibly continuous and not contain any supplementary connection to any other component. Permitted

is the fitment of an uninsulated earthing conductor between distributor body and cylinder block.

(iii) Ignition advance shall be restricted to mechanical actuation within the distributor."

 

I think that rules out that PEEL black box.

[raleigh]

Ah okay sorry, didn't quite get what you were doing.

 

Best way to kill fuel pump is get one of the little black boxes they use for LPG cars; they have a signal from your ignition coil and when the signal stops they kill the pump after 5 seconds.

 

I think the brand I used is Peak, any auto electrician should be able to hook you up.

I have done the same on another one of my race cars.(Non Rolla).I used a LPG saftey cut off switch made by PEEL.The part number is CP30.I found it necessary to use a momentery fuel pump switch to prime the DCOE webers after they had sat for a few months with this set up,This was because the Elec pump will only work when the safety switch senses the IGN Coil firing.I used a reverse current diode as well to not risk blowing up the safety switch.Have a look at the peel web site for more info.

[philbey]

"Ignition: May be of the same type, but not necessarily brand as supplied by the manufacturer for the make

and model concerned. Contact breaker points and condenser may be removed and their standard operations

performed by electronic components providing the following conditions are adhered to:

(i) All components, save for the coil, shall be an integral part of the distributor.

(ii) A maximum of two wires shall connect the low tension side of the distributor to the coil. These wires shall

be visibly continuous and not contain any supplementary connection to any other component. Permitted

is the fitment of an uninsulated earthing conductor between distributor body and cylinder block.

(iii) Ignition advance shall be restricted to mechanical actuation within the distributor."

 

I think that rules out that PEEL black box.

 

Not at all - you are not modifying the ignition system in any way; you are not adding an extra wire between the distributor and the coil, all you are doing is adding a signal wire from a single coil terminal to the peel box.

 

Trust me you won't find a simple more straightforward way to do it. Plus I've seen em on plenty of race cars.